Power lines for electric vehicles--such as the one described in German Patent n.sup.o 1.011.914 by Ludwig Reihardt, published on Jul. 11, 1957--are known to comprise an elongated insulating enclosure closed at the top by a number of conducting plates aligned in a straight direction and insulated from one another. The enclosure houses an elastically deformable conducting strip element made of ferromagnetic material, and which is attracted by the magnetic field generated by electromagnets to flex a portion of the conducting strip element towards the conducting plates to electrically supply at least one
French Patent n.sup.o 1.151.382 by Jean-Florent DE BRUYN and Jose-Gaston DE BRUYN, published on Jan. 29, 1958, describes an electric vehicle current supply system comprising a hollow elongated insulating enclosure closed at the top by a number of conducting plates aligned in the traveling direction of the vehicle and separated by insulating elements interposed between adjacent conducting plates. The enclosure houses an elastically deformable conducting strip element extending in the traveling direction of the vehicle, and having a strip portion of ferromagnetic material on which is superimposed a strip portion of good electrically conducting material. The conducting element is attracted by the magnetic field generated by electromagnets on an electric vehicle to flex a portion of the conducting strip element towards the conducting plates to electrically supply at least one.
The power lines described in the above patents employ conducting strip elements comprising a layer of elastically deformable ferromagnetic material, possibly covered with a layer of good current conducting material (such as copper). In many operating conditions, known lines fail to provide for good mechanical and electric contact between the conducting strip element and conducting plates, so that, on account of the high current carried by the conducting strip element, electric arcs may be generated between the conducting strip element and conducting plates. Besides seriously damaging the conducting strip element, such arcs may even result in fusion of a portion of the plate and the conducting element, which may subsequently remain firmly connected to the conducting plate. When this occurs, the power line is totally unusable, by the conducting strip element being prevented from flexing along the line to supply other conducting plates, and the conducting plate to which the conducting element is fused remains permanently live, thus endangering the safety of anyone approaching the line. What is more, no provision is made on known power lines for means by which to detect the above condition.